What Causes Asthma?

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Asthma affects 8% of American adults—nearly 19 million people. Almost 7 million children have asthma, too, according to the Centers for Disease Control and Prevention (CDC).

No one knows with absolute certainty what causes some people to develop asthma, but as the Asthma and Allergy Foundation of America notes, the condition does run in the family. Certain people with a family history of asthma and allergies seem predisposed to developing this chronic inflammation of the lungs, suggesting that heredity plays a role. Most experts believe a combination of genetic and environmental influences are responsible.

Recognizing Signs of an Asthma Flare-Up

Additionally, some people develop asthma in adulthood. You could be 40, 50 or even 60 years old and still develop asthma. Many cases of adult-onset asthma are linked to allergies—allergies to pets, cigarette smoke, mold and other substances are often triggers for these cases. Other cases are linked to obesity and various illnesses such as influenza. Women are also at greater risk of developing asthma as adults—some research suggests that hormonal fluctuations may play a role. 

While we don’t know exactly why asthma develops, we do know common triggers that can make symptoms worse. Asthma is different in everyone, which is why it’s important to identify your specific triggers so you can avoid them. 


Because they have very sensitive airways, people with asthma are extra sensitive to certain triggers. When you’re exposed to your particular trigger, your airways respond by swelling and getting inflamed. The muscles around them might even tighten up. These reactions make it hard to breathe. 

From the day we are born we are exposed to many different allergens. Our individual immune system processes these allergens, resulting in tolerance or sensitization. For example, you might be super-sensitive to an allergen like pollen or pet dander. You walk into the home of a friend who owns a cat and almost immediately you can feel your chest tighten up. Or your trigger could be an irritant in the air, like smoke or strong fumes.

Other triggers include:

Respiratory infections. Colds, flu and sore throats frequently precede asthma flare-ups, especially in children. To reduce your chances of contracting the flu, get a flu vaccination each autumn.  

Dust. Dust and dust mites are inevitable in your home, but that doesn’t make life any easier on people with asthma who are sensitive to them. The CDC recommends avoiding down-filled bedding and pillows and putting covers on your mattresses and pillows to create a barrier between you and those dust mites. You could also install air filters in your home and use a vacuum cleaner equipped with a HEPA filter.

Mold and mildew. Mold grows as a result of moisture in the air, and breathing in that mold can trigger an attack. Reduce the amount of humidity in the air by using a dehumidifier or air conditioner, and fix any water leaks immediately.

Cold air.  Cold, dry air is notorious for causing asthma to get worse. The cold air irritates your airways, making them shrink up, so it’s hard for you to breathe. Try to avoid spending time outside when it’s really cold.

Exercise. The technical term for this is exercise-induced bronchoconstriction. You may know it from the way your chest gets tight or your breathing becomes labored when you’re running or playing a sport. If you have this trigger, your doctor will likely prescribe an inhaled medication for you to take before exercising, such as a short-acting beta agonist (SABA) or ipratropium that will help open your airways.

Cockroaches. As if there weren’t enough reasons to hate them, cockroaches can make your asthma worse. Cockroach excrement and dust can trigger bronchial inflammation. Put your exterminator on speed dial.

Aspirin.  If your asthma gets worse after you take aspirin or another nonsteroidal anti-inflammatory drug (NSAID), you may have aspirin-induced asthma. It tends to develop after a viral infection and provokes very severe symptoms in some people. Stay far away from aspirin and NSAIDs if you know they’re a trigger.

Is your job causing your asthma?

If you’ve spent a good part of your adult life breathing in chemical fumes or other substances at work—or if you’ve been exposed to a high concentration of a particular irritant—your chance of developing what’s called occupational asthma is much higher.  And unfortunately, hundreds of substances are known to cause occupational asthma, including chemicals used to make paint and insulation, metals, chlorine gas, sulfur dioxide, plant proteins found in latex, enzymes in baking flour, and enzymes in detergents.

People with this type of asthma experience the same types of symptoms but they might also have a lot of nasal congestion and irritated eyes. While signs of “regular” asthma may come and go, occupational asthma tends to get worse as you spend more time on the job; then they let up when you have some time off. However, the Mayo Clinic warns that the longer you’re exposed to the trigger, the more likely it is that your symptoms will become chronic.

Since occupational asthma symptoms are similar to those of bronchitis, it’s not uncommon to get misdiagnosed. If you’re noticing some symptoms that just won’t go away, your doctor can help you develop a treatment plan to discuss with your employer, which may include avoiding the substance at work that’s causing your problems.

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2019 Dec 18

  1. Asthma. American Academy of Allergy, Asthma & Immunology. http://www.aaaai.org/conditions-and-treatments/asthma.aspx

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  9. Weather and Asthma. Nemours. http://kidshealth.org/parent/medical/asthma/weather_asthma.html

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